More formal:
* Apprehensive
* Anxious
* Uneasy
* On edge
* Trepidatious
* Jittery
* Agitated
* Disquieted
More informal:
* Butterflies in my stomach
* Feeling the heat
* A little shaky
* Wired
* On pins and needles
* Freaked out
* Stressed
More specific:
* Nervously excited (if the nervousness is accompanied by positive anticipation)
* Terrified (if the nervousness is extreme)
* Concerned (if the nervousness is related to worry)
* Hesitant (if the nervousness is related to doubt or uncertainty)
Figurative language:
* My heart was pounding in my chest.
* I felt like I was going to burst.
* My hands were clammy.
* I couldn't sit still.
The best phrase will depend on the specific situation and the tone you are trying to convey.